1-7
Section
Control System Principles
14
1-7-2 Control System Principles
In an open-loop system, positioning is controlled according to the number of
input pulses that the motor receives, and no position feedback is provided. The
CS1W-NC
j
13/NC
j
33 PCUs all employ pulse-output-type open-loop sys-
tems, and the most commonly used motor for this type of control system is a
stepping motor. The angle of rotation of a stepping motor can be controlled
through the number of pulse signals supplied to the motor drive. The number of
rotations of the stepping motor is proportional to the number of pulses supplied
by the PCU, and the rotational speed of the stepping motor is proportional to the
frequency of the pulse train.
Position controller
(e.g., PCU)
Pulse
train
Stepping motor or
pulse-train input-type
servo motor
Reduction gear
Turntable
Ball screw
1-7-3 Basic Positioning System Design
The following diagram and parameters illustrate a simplified positioning system.
M : Reduction ratio
P : Feed screw pitch (mm/revolution)
V : Feed velocity of object being positioned (mm/s)
θ
s
: Stepping angle per pulse (degree/pulse)
P
Stepping motor
Reduction gear
Object being
positioned
N
M
V
Feed screw pitch
The travel distance per pulse sent to the motor driver is called the “pulse rate”
and is calculated according to the following equation:
Pulse rate = P/(pulses per revolution x M)
= P/((360/
θ
s
) x M))
= (P x
θ
s
)/(360 x M)
Using the pulse rate, the number of pulses required to move the object a dis-
tance L is given by the following calculation:
No. of pulses = Travel distance
÷
Pulse rate
= L
÷
Pulse rate
= L
÷
(P x
θ
s
)/(360 x M)
= (360
×
M
×
L)/(P x
θ
s
)
The pulse speed required to move the object with a feed speed of V mm/s is
given by the following calculation:
Pulse speed = Feed speed
÷
Pulse rate
= V
÷
Pulse rate
= V
÷
(P x
θ
s
)/(360 x M)
= (360
×
M
×
V)/(P x
θ
s
)
The PCU performs positioning control by providing the number of pulses and the
pulse speed in the form of position instructions and speed instructions.
Open-Loop System
Summary of Contents for CS1W-NC113 - REV 02-2008
Page 1: ...CS1W NC113 213 413 133 233 433 Position Control Units ...
Page 2: ...iv ...
Page 4: ...vi ...
